1. Field of Invention
The present invention relates to a device and method for use in wavelength division multiplexed communications systems and systems incorporating the device. More specifically, the present invention relates to a device and method for extracting and adding information from and to wavelength division multiplexed systems, and systems incorporating the device.
2. Discussion of Related Art
Demand for optical communication systems is growing with the growing demand for faster and more reliable broadband networks. Wavelength division multiplexing (WDM) is one technique used to increase the capacity of optical communication systems. Such optical communication systems include, but are not limited to, telecommunication systems, cable television systems (CATV), and local area networks (LANs). An introduction to the field of Optical Communications can be found in “Optical Communication Systems” by Gowar, ed. Prentice Hall, N.Y., 1993.
WDM optical communication systems carry multiple optical signal channels, each channel being assigned a different wavelength. Optical signal channels are generated, multiplexed to form an optical signal comprised of the individual optical signal channels, and transmitted over a single waveguide such as an optical fiber. The optical signal is subsequently demultiplexed such that each individual channel is routed to a designated receiver.
Single or multiple optical channels can be routed to different destinations, such as in telecommunication networks, cable television subscriber systems and optical LANs. Routing is performed by selectively sending specific channels to a desired location. Such specific channels can be dropped at the desired location. In addition, another signal may be subsequently added to replace the dropped channel (alternatively, an unused channel can also be added.) This form of optical routing is generally referred to as “optical add/drop multiplexing” which is performed by an “optical add/drop multiplexer” or OADM.
Current OADMs allow a wavelength channel to be completely dropped from an optical signal. A “pay-as-you-grow” type of service paradigm is now in demand. In a metropolitan optical network utilized by telecom as well as cable systems, a higher degree of flexibility is often needed where a partial amount of a wavelength channel is required to be dropped while the remainder continues along the transmission line. Such an architecture enables wavelength sharing or wavelength broadcasting.
A higher degree of flexibility may become necessary in different situations. For instance, when traffic patterns change, drop capacity requirements may gradually increase until a complete wavelength drop may be needed at a particular location. In addition, when a service provider responds to increase demand and gradually upgrades allowed bandwidth, a smooth “in service” upgrade along a distribution path may require more wavelength channels to be dropped during the upgrading period. Furthermore, a more flexible content distribution scheme may require each location to have the capability of adding more channels carrying information to be transported to other locations.